Spectroscopic imaging combines digital imaging and molecular spectroscopy techniques, which can include Raman scattering, fluorescence, photoluminescence, ultraviolet, visible and infrared absorption spectroscopies. When applied to the chemical analysis of materials, spectroscopic imaging is commonly referred to as chemical imaging. Instruments for performing spectroscopic (i.e., chemical) imaging typically comprise image gathering optics, focal plane array imaging detectors and imaging spectrometers.
In general, the sample size determines the choice of image gathering optic. For example, a microscope is typically employed for the analysis of sub micron to millimeter spatial dimension samples. For larger objects, in the range of millimeter to meter dimensions, macro lens optics are appropriate. For samples located within relatively inaccessible environments, flexible fiberscopes or rigid borescopes can be employed. For very large scale objects, such as planetary objects, telescopes are appropriate image gathering optics.
Often the sample under study includes a plurality of species in a mixture. Thus, the chemical image of the sample characterizes the sample as a mixture of species. Each specie can be a pure element, a compound of said element with other elements or a compound. While the chemical image of the sample can identify each of the species by using color or some other indication, it fails to communicate the spectral image of each specie independent of the mixture. Thus, there is a need for a method and apparatus to interactively obtain the spectral image for the desired specie from a chemical image of the mixture.
The instant disclosure addresses the needs described above. In one embodiment, the disclosure relates to a method of obtaining a spectral image of each of a plurality of predetermined chemical species in a sample, comprising: (a) illuminating the sample with a first plurality of photons to produce a second plurality of photons; (b) collecting the second plurality of photons and producing a plurality of images of the sample using those photons, wherein each of the images comprises a frame consisting essentially of a plurality of pixels; (c) for each of the predetermined chemical species, identifying at least one wavelength range at which the chemical specie exhibits a unique absorption of radiation; (d) identifying at least one wavelength range at which none of the predetermined chemical species exhibits an absorption of radiation; (e) in each of the image frames, identifying which of the pixels do not contain any of the predetermined chemical species; (f) in each of the image frames, identifying which pixels contain only one of the predetermined chemical species; (g) repeating the previous step for each of the predetermined chemical species; (h) in each of the image frames, identifying which pixels contain more than one of the predetermined chemical species; (i) for each pixel that contains more than one chemical species, separating the contribution of each of chemical species; and (j) composing separate spectral images of each of predetermined chemical species in the sample.
In another embodiment, the instant disclosure relates to an apparatus for obtaining a spectral image of each of a plurality of predetermined chemical species in a sample, comprising: (a) an illumination source for illuminating the sample with a first plurality of photons to form a second plurality of photons; (b) an optical device for receiving and directing the second plurality of photons to an imaging device; (c) an imaging device for forming a plurality of images of the sample, each of the images comprising a frame consisting essentially of a plurality of pixels; and (d) a processor in communication with the imaging device and being adapted to: (i) for each predetermined chemical species, identifying at least one wavelength range at which the chemical specie exhibits a unique absorption of radiation; (ii) identifying at least one wavelength range at which none of the predetermined chemical species exhibits an absorption of radiation; (iii) in each of the image frames, identifying which pixels do not contain any of the predetermined chemical species; (iv) in each of the image frames, identifying which pixels contain only a first predetermined chemical species; (v) repeating this step for each of the predetermined chemical species; (vi) in each of the image frames, identifying which pixels contain more than one of the predetermined chemical species; (vii) for each pixel that contains more than one predetermined chemical species, separating the contribution of each predetermined chemical species; and (viii) composing separate spectral images of each predetermined chemical species in the sample.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed.